1. Field of the Invention
The present invention relates to an organic electric field light-emitting (EL) display device having, for each pixel, an organic electric field light-emitting (EL) element adapted to emit light when a current flows through its organic multilayer film between two electrodes as a result of application of an electric field between the two electrodes.
2. Description of the Related Art
An organic EL display device (organic EL display) has a display panel which includes a display section and drive section of the display section. The display section has a plurality of pixel circuits arranged in a matrix. The display panel is manufactured by forming the display and drive sections on a single substrate using the semiconductor technology which includes the TFT (thin film transistor) forming process. Alternatively, the drive circuits of the display panel are supplied by a flexible substrate, and the substrate and display panel are electrically connected together.
Various types of circuits are proposed for use as a pixel circuit of the organic EL display to prevent image quality degradation caused by the variation in characteristics of the TFTs in the pixel circuits.
Major and well known among the proposed types of circuits are the 4T/1C pixel circuit with four transistors (4T) and one capacitor (1C) as well as 4T/2C, 5T/1C and 3T/1C pixel circuits.
All of the above pixel circuits incorporate a correction circuit adapted to control the current flow through the organic EL element at a constant level. As a result, the potential of one of the electrodes of the organic EL element is controlled according to the variation in characteristics. In contrast, at the other electrodes, a common potential such as ground voltage is applied commonly to a plurality of pixels of a pixel section.
Therefore, the potential of one of the electrodes is corrected to a certain extent. However, the potential of the other electrode (e.g., ground voltage) remains uncorrected. As a result, image quality degradation such as shading or crosstalk manifests itself in the event of a variation in potential of the other electrode in the pixel section.
Here, if shading or crosstalk occurs, a voltage drop in a power line, adapted to supply positive power to the organic EL element, is typically often regarded as a problem. However, such image quality degradation also occurs due to the variation in negative power such as the ground voltage.
Shading is a phenomenon in which the pixel (more specifically, organic EL element) brightness changes gradually between the pixels closer to and farther from the power source in the display rows (horizontal arrangement of the pixels) of the pixel section. If the common potential such as ground voltage is non-uniform to such an extent that it rises gradually with increasing distance from the power source, shading manifests itself on the display image in a more intense manner.
On the other hand, in the case in which shading does not occur, even if two adjacent pixels of interest in the adjacent rows far from the power source attempt to emit the same brightness, crosstalk may manifest itself. Crosstalk is a phenomenon in which if the drive current consumption from the power source to the pixel of interest is different between the adjacent pixel rows to which the two pixels of interest belong, the pixel of interest in the pixel row which consumes more drive current appears darker than that in the pixel row which consumes less drive current. If the common potential such as ground voltage is non-uniform to such an extent that it rises gradually with increasing distance from the power source, crosstalk manifests itself on the display image in a more intense manner.
In order to prevent uneven display such as shading and crosstalk, the provision of an auxiliary wiring is proposed which is lower in resistance than the common electrode of the organic EL element, i.e., the upper electrode (refer, for example, to Japanese Patent Laid-Open Nos. 2001-195008, 2002-318553 and 2004-207217 (hereinafter referred to as Patent Documents 1, 2 and 3)).
In Patent Documents 1 to 3, an auxiliary wiring is disclosed which is formed in the vicinity of the pixel border. This wiring is disposed in a grid-like arrangement and surrounds a pixel opening portion. A wiring disposed in such a grid-like arrangement will be hereinafter particularly referred to as a power auxiliary grid line.
In Patent Document 2, on the other hand, another auxiliary wiring disposed in a ring-like arrangement (referred to as a second electrode power line in Patent Document 2) is provided which is electrically connected to the power auxiliary grid line and surrounds the pixel arrangement region. This auxiliary wiring in a ring-like arrangement will be hereinafter referred to as a power auxiliary circumferential line.